Conversion method and conversion apparatus

ABSTRACT

A conversion method for converting luminance of a video, including a luminance value in a first luminance range, to be displayed on a display apparatus includes: acquiring a first luminance signal indicating a code value obtained by quantization of the luminance value of the video; and converting the code value indicated by the acquired first luminance signal into a second luminance value determined based on a luminance range of the display apparatus, the second luminance value being compatible with a second luminance range with a maximum value smaller than a maximum value of the first luminance range and larger than 100 nit. This provides the conversion method capable of achieving further improvement.

BACKGROUND 1. Technical Field

The present disclosure relates to a conversion method and conversionapparatus regarding luminance of a video.

2. Description of the Related Art

Conventionally, an image signal processing apparatus for improving adisplayable luminance level is disclosed (for example, refer toUnexamined Japanese Patent Publication No. 2008-167418).

SUMMARY

The above-described conventional technology needs further improvement.

In one general aspect, the techniques disclosed here feature aconversion method for converting luminance of a video to be displayed ona display apparatus, the conversion method including: acquiring a firstluminance signal indicating a first code value obtained by quantizationof the luminance value of the video, the luminance value of the videobeing included in a first luminance range; and converting the first codevalue indicated by the acquired first luminance signal into a secondluminance value compatible with a second luminance range, a maximumvalue of the second luminance range being determined based on aluminance range of the display apparatus, the maximum value of thesecond luminance range being smaller than a maximum value of the firstluminance range, and the maximum value of the second luminance rangebeing larger than 100 nit.

Note that these general or specific aspects may be implemented using anapparatus, a system, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or may beimplemented using an arbitrary combination of an apparatus, a system, amethod, a computer program, and a recording medium.

The above-described aspect can achieve further improvement.

Note that further effects and advantages of the present disclosure willbe apparent from the disclosed details of the present specification andthe drawings. The above-described further effects and advantages may beindividually provided by various exemplary embodiments and featuresdisclosed in the present specification and the drawings, and all theeffects and advantages do not necessarily need to be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating evolution of video techniques;

FIG. 2 is a diagram illustrating a relationship among video production,delivery schemes, and display apparatus in introduction of new videorepresentation into content;

FIG. 3 is a diagram illustrating a relationship among masters, deliveryschemes, and display apparatuses in introducing HDR;

FIG. 4A is a diagram illustrating SDR display processing within an SDRTV;

FIG. 4B is a diagram illustrating the SDR display processing within theSDR TV with peak luminance of 300 nit;

FIG. 5 is a diagram illustrating conversion from HDR to SDR;

FIG. 6A is a diagram illustrating case 1 where an HDR disc stores onlyan HDR-enabled HDR signal;

FIG. 6B is a diagram illustrating case 2 where an HDR disc stores anHDR-enabled HDR signal and an SDR-enabled SDR signal;

FIG. 7 is a diagram illustrating conversion processing from HDR topseudo HDR;

FIG. 8A is a diagram illustrating an example of an electro-opticaltransfer function (EOTF) that supports each of HDR and SDR;

FIG. 8B is a diagram illustrating an example of inverse EOTF thatsupports each of HDR and SDR;

FIG. 9 is an illustrative diagram of a determination method of a codevalue of a luminance signal to be stored in content, and a process ofrestoring a luminance value from the code value during playback;

FIG. 10A is a diagram illustrating one example of display processing toconvert an HDR signal and to perform HDR display within an HDR TV;

FIG. 10B is a diagram illustrating one example of display processing toperform HDR display using an HDR-enabled playback apparatus and the SDRTV;

FIG. 10C is a diagram illustrating one example of display processing toperform HDR display using the HDR-enabled playback apparatus and the SDRTV connected to each other via a standard interface;

FIG. 11 is a block diagram illustrating a configuration of a conversionapparatus and a display apparatus according to an exemplary embodiment;

FIG. 12 is a flowchart illustrating a conversion method and a displaymethod to be performed by the conversion apparatus and the displayapparatus according to the exemplary embodiment;

FIG. 13A is a diagram illustrating first luminance conversion;

FIG. 13B is a diagram illustrating another example of the firstluminance conversion;

FIG. 14 is a diagram illustrating second luminance conversion;

FIG. 15 is a flowchart illustrating detailed processing of displaysettings;

FIG. 16 is a diagram illustrating third luminance conversion;

FIG. 17 is a diagram illustrating conversion processing from HDR topseudo HDR;

FIG. 18 is a diagram illustrating a playback operation of a dual disc;and

FIG. 19 is a flowchart illustrating the playback operation of a dualdisc.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

The inventor of the present disclosure has found out that the followingproblem occurs regarding the image signal processing apparatus describedin the column of “BACKGROUND ART”.

The image signal processing apparatus disclosed in Unexamined JapanesePatent Publication No. 2008-167418 calculates linear luminance for eachpixel based on linear RGB values calculated from pixels that constitutea subject, calculates corrected linear luminance for each pixel andcorrected linear RGB values of combined pixels obtained by combining aplurality of pixels that include the pixel based on the linear RGBvalues and the linear luminance, and then applies gamma correction toeach of the corrected linear luminance and the corrected linear RGBvalues to calculate luminance for display and RGB values for display.Thus, the image signal processing apparatus achieves increase in anumber of displayable gradations by correcting the linear luminancebased on the corrected linear RGB values.

However, correction (conversion) of luminance in the image signalprocessing apparatus and the like disclosed in Unexamined JapanesePatent Publication No. 2008-167418 does not take into consideration aluminance conversion method for correcting (converting) luminance from afirst luminance range to a second luminance range of which the luminancerange is reduced.

In order to solve the above-described problem based on the aboveexamination, the inventor of the present disclosure has examined thefollowing improvement measure.

A conversion method according to one aspect of the present disclosure isa conversion method including: acquiring a first luminance signalindicating a first code value obtained by quantization of the luminancevalue of the video, the luminance value of the video being included in afirst luminance range; and converting the first code value indicated bythe acquired first luminance signal into a second luminance valuecompatible with a second luminance range, a maximum value of the secondluminance range being determined based on a luminance range of thedisplay apparatus, the maximum value of the second luminance range beingsmaller than a maximum value of the first luminance range, and themaximum value of the second luminance range being larger than 100 nit.

This allows appropriate conversion of the luminance in the firstluminance range into luminance in the second luminance range with areduced luminance range.

In addition, for example, the converting the first code value mayinclude: by using an electro-optical transfer function (EOTF) thatassociates the luminance value in the first luminance range with aplurality of first code values, determining a first luminance valueassociated with the first code value indicated by acquired firstluminance signal, the first luminance value being compatible with thefirst luminance range, I determining the second luminance valueassociated with the first luminance value in advance, the secondluminance value being compatible with the second luminance range; andperforming first luminance conversion to convert the first luminancevalue compatible with the first luminance range into the secondluminance value compatible with the second luminance range.

In addition, for example, the maximum value of the second luminancerange may be a maximum value of the luminance range of the displayapparatus, and the performing the first luminance conversion mayinclude, when the first luminance value is a first maximum luminancevalue that is a maximum value of the luminance values of a plurality ofimages that constitute the video, determining a second maximum luminancevalue that is the maximum value of the luminance of the displayapparatus as the second luminance value.

In addition, for example, the performing the first luminance conversionmay include: when the first luminance value is equal to or less than anaverage luminance value that is an average of the luminance values ofthe plurality of images that constitute the video, determining the firstluminance value as the second luminance value; and when the firstluminance value is equal to or greater than the first maximum luminancevalue, determining the second maximum luminance value as the secondluminance value.

In addition, for example, the performing the first luminance conversionmay include, when the first luminance value is between the averageluminance value and the first maximum luminance value, determining thesecond luminance value corresponding to the first luminance value byusing a natural logarithm.

Furthermore, for example, luminance information including at least oneof the first maximum luminance value and an average luminance value thatis an average of the luminance values of the plurality of images thatconstitute the video may be acquired as metadata information of thevideo.

Furthermore, for example, the first luminance signal may be acquiredfrom a recording medium, and luminance information including at leastone of the first maximum luminance value and an average luminance valuethat is an average of the luminance values of the plurality of imagesthat constitute the video may be acquired via a network.

Furthermore, for example, luminance information corresponding to each ofa plurality of scenes of the video may be further acquired, for each ofthe scenes, the luminance information including at least one of thefirst maximum luminance value that is a maximum value of the luminancevalues of the plurality of images that constitute each of the scenes,and an average luminance value that is an average of the luminancevalues of the plurality of images that constitute each of the scenes.Performing the first luminance conversion may include, for each of theplurality of scenes, determining the second luminance value according tothe luminance information corresponding to each of the scenes.

Furthermore, for example, a third luminance value associated with thesecond luminance value in advance may be determined, the third luminancevalue being compatible with a third luminance range with a maximum valueof 100 nit; second luminance conversion may be performed to convert thesecond luminance value compatible with the second luminance range intothe third luminance value compatible with the third luminance range; thethird luminance value may be quantized by using an inverse EOTF thatassociates a luminance value in the third luminance range with aplurality of second code values; the second code values obtained by thequantization may be determined; the third luminance value compatiblewith the third luminance range may be converted into the third luminancesignal indicating the determined second code value; and the thirdluminance signal may be output to the display apparatus.

In addition, for example, the performing the second luminance conversionmay include: determining a luminance value associated with the secondluminance value as the third luminance value by using luminance-relatedinformation according to display characteristic information that isinformation indicating a display characteristic of the displayapparatus; and switching luminance conversion processing according tothe display characteristic information.

In addition, for example, the display characteristic information may bea display mode of the display apparatus, the performing the secondluminance conversion may include: when the display mode is a normalmode, performing luminance conversion to convert the third luminancevalue into a direct proportion value in direct proportion to the secondluminance value; and when the display mode is a dynamic mode in which ahigh-luminance pixel becomes brighter and a low-luminance pixel becomesdarker than pixels in the normal mode, performing luminance conversionto convert the third luminance value of the low-luminance pixel into avalue higher than the direct proportion value in direct proportion tothe second luminance value, and to convert the third luminance value ofthe high-luminance pixel into a value lower than the direct proportionvalue in direct proportion to the second luminance value.

In addition, for example, the performing the first luminance conversionmay include determining the second maximum luminance value by usingdisplay characteristic information that is information indicating adisplay characteristic of the display apparatus.

Furthermore, for example, the display characteristic information may beacquired from the display apparatus.

In addition, for example, the acquiring the display characteristicinformation may be performed immediately before the converting the codevalue.

In addition, for example, the acquiring the display characteristicinformation may be performed at timing of first connection with thedisplay apparatus.

Note that these general or specific aspects may be implemented using anapparatus, a system, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or may beimplemented using any combination of a system, a method, an integratedcircuit, a computer program, or a recording medium.

The display method and the display apparatus according to one aspect ofthe present disclosure will be specifically described below withreference to the accompanying drawings.

Exemplary embodiments described below indicate one specific example ofthe present disclosure. Numerical values, shapes, materials,dispositions and connection forms of the components, steps, order of thesteps, and the like that are indicated in the following exemplaryembodiments are one example, and do not intend to limit the presentdisclosure. Also, among the components described in the followingexemplary embodiments, components that are not described in anindependent claim which represents the highest concept are described asoptional components.

Exemplary Embodiment

The present disclosure relates to an image conversion-playback methodand apparatus for displaying a high dynamic range (HDR) signal, which isa high-luminance signal with a high luminance range, in a displayapparatus, such as a TV, projector, tablet, and smart phone, the displayapparatus supporting a standard dynamic range (SDR) signal, which is anormal luminance signal having a luminance range with a maximumluminance value of 100 nit.

[1-1. Background]

First, transition of video techniques will be described with referenceto FIG. 1. FIG. 1 is a diagram illustrating evolution of the videotechniques.

Until now, high definition of video has focused on increase in a numberof display pixels. So-called 2K video is widely used, from 720×480-pixelStandard Definition (SD) video to 1920×1080-pixel High Definition (HD)video.

In recent years, introduction of so-called 4K video has started with aview toward higher definition of video, including 3840×1920-pixel UltraHigh Definition (UHD) video and 4096×1920-pixel 4K video.

In addition to high resolution of video through introduction of 4K,consideration is given to high definition of video through extension ofa dynamic range, enlargement of a color gamut, and addition orimprovement of a frame rate.

Among those improvements, regarding the dynamic range, HDR (High DynamicRange) attracts attention as a scheme that supports a luminance rangewith an extended maximum luminance value for representing bright lightincluding specular reflection light that cannot be represented bycurrent TV signals with brightness more similar to actual brightnesswhile maintaining dark area gradation in conventional video.Specifically, while a scheme of the luminance range supported byconventional TV signals is referred to as SDR (Standard Dynamic Range)with the maximum luminance value of 100 nit, HDR is assumed to extendthe maximum luminance value to 1,000 nit or more. Standardization of HDRis under way in organizations such as SMPTE (Society of Motion Picture &Television Engineers) and ITU-R (International Telecommunications UnionRadiocommunications Sector).

Assumed specific application of HDR includes broadcast, package media(such as Blu-ray (registered trademark) disc), and Internet delivery,similarly to HD and UHD.

Hereinafter, in an HDR-enabled video, luminance of the video includes aluminance value within the luminance range of HDR. A luminance signalobtained through quantization of the luminance value of the video isreferred to as an HDR signal. In an SDR-enabled video, luminance of thevideo includes a luminance value within the luminance range of SDR. Aluminance signal obtained through quantization of the luminance value ofthe video is referred to as an SDR signal.

[1-2. Relationship Among Master Generation, Delivery Schemes, andDisplay Apparatuses]

FIG. 2 is a diagram illustrating a relationship among video production,delivery schemes, and display apparatus in introduction of new videorepresentation into content.

When new video representation (increase in a number of pixels or thelike) is introduced for high definition of video, as illustrated in FIG.2, it is necessary to (1) change a master for home entertainment use ona video production side. Accordingly, it is also necessary to (2) renewthe delivery schemes, such as broadcast, communication, and packagemedia, and to (3) renew the display apparatus, such as a TV, projector,and the like, that displays the video.

[1-3. Relationship Among Masters, Delivery Schemes, and DisplayApparatuses in Introducing HDR]

In order that a user enjoys at home content that supports new videorepresentation (for example, high-luminance video content (HDRcontent)), it is necessary to newly introduce both an HDR-enableddelivery scheme and an HDR-enabled display apparatus. That is, in orderto enjoy at home the content that supports the new video representation,the user needs to prepare the delivery scheme and the display apparatusthat support the new video representation. This is also unavoidable whennew video representation is introduced, such as when videorepresentation is changed from SD videos to HD videos, from HD videos tothree-dimensional (3D) videos, and from HD videos to ultra highdefinition (UHD, 4K) videos.

For this reason, change to the new video representation, which needsreplacement purchase of a TV which is expensive and does not allow easyreplacement in terms of size, weight, etc., will be dependent on wideruse of the display apparatus having new functions (for example, a TV).Since a medium side and content side are also unable to make largeinvestment at first, the new video representation comes into wide useslowly in many cases.

Therefore, as illustrated in FIG. 3, regarding HDR as well, it isexpected that replacement purchase of a TV (hereinafter referred to as“HDR TV”) that supports HDR-enabled video display (hereinafter referredto as “HDR display”) is required in order to take full advantage oforiginal video representation of HDR.

[1-4. SDR TV]

A TV (hereinafter referred to as “SDR TV”) that supports only display ofan SDR-enabled video display (hereinafter referred to as “SDR display”)normally receives an input signal with a luminance value of up to 100nit. Accordingly, the SDR TV with display capability of 100 nit issufficient for representing the luminance value of the input signal.However, many of the SDR TVs actually have a function of playing a videowith an optimal luminance value adapted to viewing environments (darkroom: cinema mode, bright room: dynamic mode, etc.), and have capabilityof video representation of 200 nit or more. That is, such an SDR TV candisplay a video with up to maximum luminance of display capability (forexample, 300 nit) by selecting a display mode according to the viewingenvironment.

However, since a luminance upper limit of the SDR-scheme input signalthat is input into the SDR TV is determined as 100 nit, as long as aconventional SDR-scheme input interface is used, it is difficult to usehigh-luminance video playback capability of the SDR TV exceeding 100 nitfor playback of the HDR signal (refer to FIG. 4A and FIG. 4B).

[1-5. HDR to SDR Conversion]

It is assumed that high-luminance video content (hereinafter referred toas “HDR content” or “HDR video”) is output from the SDR TV via anHDR-enabled playback apparatus (for example, communication set top box(STB), Blu-ray device, IPTV playback apparatus), the high-luminancevideo content being delivered by delivery schemes such as HDR-enabledbroadcast, video delivery via communication networks, or HDR-enabledpackage media (for example, HDR-enabled Blu-ray disc). When the SDR TVplays the HDR content, “HDR to SDR conversion” is implemented forconverting the HDR-enabled HDR signal into the SDR signal in the SDRluminance range with a maximum value of 100 nit such that the SDR TV candisplay the video correctly. This allows the SDR TV to display the SDRvideo obtained by conversion from the HDR video by using the convertedSDR signal (refer to FIG. 5).

However, even in this case, although the user has purchased theHDR-enabled content (for example, Blu-ray disc, HDR IPTV content) andHDR-enabled playback apparatus (for example, Blu-ray device, HDR-enabledIPTV playback apparatus), the user can enjoy a video only in SDR videorepresentation (SDR representation) on the SDR TV. That is, even if theHDR content and HDR-enabled playback apparatus are prepared, when thereis no HDR-enabled display apparatus (for example, HDR TV) and there isonly the SDR TV, the user cannot view the video in HDR videorepresentation (HDR representation).

Therefore, if the user cannot prepare the HDR TV, even if the userpurchases the HDR content or transmission media (playback apparatus),the user does not understand values of HDR (that is, superiority of highdefinition HDR over SDR). Thus, since the user does not understand thevalues of HDR without the HDR TV, wide use of the HDR content orHDR-enabled delivery scheme is decided depending on a speed at which HDRTVs come into wide use.

[1-6. Two Schemes of Implementing HDR to SDR Conversion]

When the HDR signal is sent to a TV by using a Blu-ray disc (BD), thefollowing two cases can be assumed as illustrated in FIG. 6A and FIG.6B. FIG. 6A is a diagram illustrating case 1 where an HDR-enabled BDstores only an HDR-enabled HDR signal. FIG. 6B is a diagram illustratingcase 2 where an HDR-enabled BD stores an HDR-enabled HDR signal and anSDR-enabled SDR signal.

As illustrated in FIG. 6A, in case 1 where the HDR TV displays a videoobtained by the Blu-ray device playing a BD, the Blu-ray device outputsa luminance signal stored in the BD to the HDR TV as it is withoutconversion, regardless of whether the Blu-ray device plays theHDR-enabled BD (hereinafter referred to as “HDR BD”) or SDR-enabled BD(hereinafter referred to as “SDR BD”). Then, the HDR TV, which canperform display processing of both the HDR signal and the SDR signal,performs display processing in accordance with the input luminancesignal, and displays the HDR video or SDR video.

On the other hand, in case 1 where the SDR TV displays a video obtainedby the Blu-ray device playing a BD, when the HDR BD is played, theBlu-ray device performs conversion processing to convert the HDR signalinto the SDR signal, and then outputs the SDR signal obtained by theconversion processing to the SDR TV. Meanwhile, when the SDR BD isplayed, the Blu-ray device outputs the SDR signal stored in the BD tothe SDR TV as it is without conversion. Accordingly, the SDR TV displaysthe SDR video.

In addition, as illustrated in FIG. 6B, case 2 where the HDR TV displaysthe video obtained by the Blu-ray device playing the BD is similar tocase 1.

On the other hand, in case 2 where the SDR TV displays a video obtainedby the Blu-ray device playing the BD, the Blu-ray device outputs the SDRsignal stored in the BD to the SDR TV as it is without conversion,regardless of whether the Blu-ray device plays the HDR BD or the SDR BD.

In both case 1 and case 2, even if the user purchases the HDR BD and theHDR-enabled Blu-ray device, the user can enjoy only the SDR videowithout the HDR TV. Therefore, the user needs the HDR TV in order toview the HDR video, and it is estimated that wide use of HDR-enabledBlu-ray device or HDR BD takes time.

[1-7. HDR to Pseudo HDR Conversion]

Accordingly, in order to accelerate wide use of HDR, it may be said tobe important that commercialization of HDR content and delivery schemecan be promoted without waiting for wide use of the HDR TV. For thispurpose, if it is possible to enable viewing of the HDR signal on theexisting SDR TV, not as the SDR video but as the HDR video or pseudo HDRvideo that is more similar to the HDR video than to the SDR video, theuser can view the higher definition video similar to the HDR videoapparently different from the SDR video, without purchasing the HDR TV.That is, if the user can view the pseudo HDR video on the SDR TV, onlyby preparing the HDR content and HDR delivery device, the user can viewthe video with higher definition than that of the SDR video withoutpreparing the HDR TV. In short, enabling viewing of the pseudo HDR videoon the SDR TV can become motivation of the user to purchase the HDRcontent or HDR delivery device (refer to FIG. 7).

In order to implement display of the pseudo HDR video on the SDR TV, itis necessary to implement “HDR to pseudo HDR conversion processing” thatmakes it possible to generate the pseudo HDR signal for displaying thevideo with maximum luminance of display capability of the SDR TV, forexample, the video of 200 nit or more and to send the generated pseudoHDR signal to the SDR TV, by using input of the video signal with amaximum value of 100 nit into the SDR TV instead of conversion of theHDR signal into the SDR video signal so that the SDR TV can correctlydisplay the video of the HDR content when the HDR content is played witha configuration in which the SDR TV is connected to the HDR deliveryscheme.

[1-8. About EOTF]

Here, EOTF will be described with reference to FIG. 8A and FIG. 8B.

FIG. 8A is a diagram illustrating an example of an electro-opticaltransfer function (EOTF) that supports each of HDR and SDR.

EOTF is commonly called a gamma curve, indicates correspondence betweena code value and a luminance value, and converts the code value into theluminance value. That is, EOTF is correspondence information thatindicates the correspondence between a plurality of code values and theluminance value.

FIG. 8B is a diagram illustrating an example of inverse EOTF thatsupports each of HDR and SDR.

Inverse EOTF indicates correspondence between the luminance value andthe code value, and quantizes and converts the luminance value into thecode value, inversely to EOTF. That is, inverse EOTF is correspondenceinformation that indicates the correspondence between the luminancevalue and the plurality of code values. For example, in a case ofrepresenting a luminance value of an HDR-enabled video with a code valueof 10-bit gradation, the luminance value in the luminance range of HDRof up to 10,000 nit is quantized and mapped to 1024 integral values from0 to 1023. That is, the luminance value (luminance value of theHDR-enabled video) in the luminance range of up to 10,000 nit isconverted into the HDR signal of a 10-bit code value by quantizationbased on inverse EOTF. In HDR-enabled EOTF (hereinafter referred to as“EOTF of HDR”) or HDR-enabled inverse EOTF (hereinafter referred to as“inverse EOTF of HDR”), it is possible to represent the luminance valuehigher than the luminance value in SDR-enabled EOTF (hereinafterreferred to as “EOTF of SDR”) or SDR-enabled inverse EOTF (hereinafterreferred to as “inverse EOTF of SDR”). For example, in FIG. 8A and FIG.8B, the maximum value of luminance (peak luminance) is 10,000 nit. Thatis, the luminance range of HDR includes the entire luminance range ofSDR, and the peak luminance of HDR is larger than the peak luminance ofSDR. The luminance range of HDR is the luminance range with the maximumvalue enlarged from 100 nit, which is the maximum value of the luminancerange of SDR, to 10,000 nit.

For example, one example of EOTF of HDR and inverse EOTF of HDR is SMPTE2084 standardized by the United States Society of Motion Picture andTelevision Engineers (SMPTE).

[1-9. How to Use EOTF]

FIG. 9 is an illustrative diagram of a determination method of a codevalue of the luminance signal to be stored in content, and a process ofrestoring the luminance value from the code value during playback.

The luminance signal indicating luminance in this example is anHDR-enabled HDR signal. An image after grading is quantized by inverseEOTF of HDR, and the code value corresponding to the luminance value ofthe image is determined. Processing such as image coding is performedbased on this code value, and a video stream is generated. Duringplayback, a decoding result of the stream is converted into a linearsignal through inverse quantization based on EOTF of HDR, and theluminance value for each pixel is restored. Hereinafter, quantization ofHDR using inverse EOTF is referred to as “inverse EOTF conversion ofHDR”. Inverse quantization of HDR using EOTF is referred to as “EOTFconversion of HDR”. Similarly, quantization of SDR using inverse EOTF isreferred to as “inverse EOTF conversion of SDR”. Inverse quantization ofSDR using EOTF is referred to as “EOTF conversion of SDR”.

[1-10. Necessity for Pseudo HDR]

Next, necessity for pseudo HDR will be described with reference to FIG.10A to FIG. 10C.

FIG. 10A is a diagram illustrating an example of display processing forconverting an HDR signal and performing HDR display within an HDR TV.

As illustrated in FIG. 10A, in displaying an HDR video, a maximum valueof the luminance range of HDR (peak luminance (HPL (HDR Peak Luminance):example 1500 nit)) may not be displayed as it is even if the displayapparatus is an HDR TV. In this case, luminance conversion is performedto adapt a linear signal after inverse quantization using EOTF of HDR toa maximum value of the luminance range of the display apparatus (peakluminance (DPL (Display Peak luminance): example 750 nit)). Then,inputting a video signal obtained through the luminance conversion intothe display apparatus allows for displaying the HDR video adapted to themaximum luminance range which is a limit of the display apparatus.

FIG. 10B is a diagram illustrating an example of display processing forperforming HDR display by using an HDR-enabled playback apparatus andSDR TV.

As illustrated in FIG. 10B, in displaying the HDR video, when thedisplay apparatus is an SDR TV, by making use of the fact that themaximum value of the luminance range of the SDR TV for display (peakluminance (DPL: example 300 nit)) exceeds 100 nit, “EOTF conversion ofHDR” performed in the HDR TV and “luminance conversion” using DPL(example: 300 nit), which is the maximum value of the luminance range ofthe SDR TV, are performed in the “HDR to pseudo HDR conversionprocessing” within the HDR-enabled playback apparatus (Blu-ray device)of FIG. 10B. If a signal obtained by performing the “luminanceconversion” can be input directly into the “display apparatus” of theSDR TV, an effect identical to the effect of the HDR TV can be achievedeven if the SDR TV is used.

However, this cannot be achieved because the SDR TV does not have meansfor performing direct input of such a signal from outside.

FIG. 10C is a diagram illustrating an example of display processing forperforming HDR display using the HDR-enabled playback apparatus and SDRTV connected to each other via a standard interface.

As illustrated in FIG. 10C, it is necessary to input into the SDR TV asignal that provides the effect of FIG. 10B by using an input interfaceusually included in the SDR TV (such as HDMI (registered trademark)). Inthe SDR TV, the signal that is input via the input interface passesthrough “EOTF conversion of SDR”, “luminance conversion for each mode”,and “display apparatus” sequentially, and displays a video adapted tothe maximum luminance range value of the display apparatus. Therefore,within the HDR-enabled Blu-ray device, a signal (pseudo HDR signal) isgenerated for cancelling “EOTF conversion of SDR” and “luminanceconversion for each mode” through which the signal passes immediatelyafter the input interface in the SDR TV. That is, within the HDR-enabledBlu-ray device, by performing “inverse luminance conversion for eachmode”, and “inverse EOTF conversion of SDR” immediately after “EOTFconversion of HDR” and “luminance conversion” using the peak luminance(DPL) of the SDR TV, a pseudo effect identical to the effect in a casewhere a signal immediately after the “luminance conversion” is inputinto the “display apparatus” (dashed arrow of FIG. 10C) is achieved.

[1-11. Conversion Apparatus and Display Apparatus]

FIG. 11 is a block diagram illustrating a configuration of theconversion apparatus and display apparatus according to the exemplaryembodiment. FIG. 12 is a flowchart illustrating the conversion methodand display method to be performed by the conversion apparatus anddisplay apparatus according to the exemplary embodiment.

As illustrated in FIG. 11, conversion apparatus 100 includes HDR EOTFconverter 101, luminance converter 102, inverse luminance converter 103,and inverse SDR EOTF converter 104. Display apparatus 200 includesdisplay setting unit 201, SDR EOTF converter 202, luminance converter203, and display unit 204.

Detailed description of each component of conversion apparatus 100 anddisplay apparatus 200 will be made in description of the conversionmethod and the display method.

Hereinafter, the luminance range of HDR (0 to HPL [nit]) is referred toas “first luminance range”. The luminance range of a display (0 to DPL[nit]) is referred to as “second luminance range”. The luminance rangeof SDR (0 to 100 [nit]) is referred to as “third luminance range”.

[1-12. Conversion Method and Display Method]

The conversion method to be performed by conversion apparatus 100 willbe described with reference to FIG. 12. Note that the conversion methodincludes step S101 to step S104 described below.

First, HDR EOTF converter 101 of conversion apparatus 100 acquires theHDR video on which inverse EOTF conversion of HDR is performed. HDR EOTFconverter 101 of conversion apparatus 100 performs EOTF conversion ofHDR on the HDR signal of the acquired HDR video (S101). Accordingly, HDREOTF converter 101 converts the acquired HDR signal into a linear signalthat indicates the luminance value. An example of EOTF of HDR is SMPTE2084.

Next, luminance converter 102 of conversion apparatus 100 performs firstluminance conversion that converts the linear signal converted by HDREOTF converter 101 by using display characteristic information andcontent luminance information (S102). In the first luminance conversion,the luminance value compatible with the luminance range of HDR(hereinafter referred to as “luminance value of HDR”), which is thefirst luminance range, is converted into the luminance value compatiblewith the luminance range of the display (hereinafter referred to as“display luminance value”), which is the second luminance range. Detailswill be described later.

From the aforementioned description, HDR EOTF converter 101 functions asan acquisition unit that acquires the HDR signal as a first luminancesignal indicating the code value obtained by quantization of theluminance value of a video. In addition, HDR EOTF converter 101 andluminance converter 102 function as a converter that converts the codevalue indicated by the HDR signal acquired by the acquisition unit intothe display luminance value compatible with the luminance range of thedisplay determined based on the luminance range of the display (displayapparatus 200), which is a maximum value (DPL) smaller than a maximumvalue (HPL) of the luminance range of HDR and larger than 100 nit.

More specifically, in step S101, HDR EOTF converter 101 uses theacquired HDR signal and EOTF of HDR to determine the luminance value ofHDR associated with the code value of HDR by EOTF of HDR, the code valueof HDR being a first code value indicated by the acquired HDR signal.Note that the HDR signal indicates the code value of HDR obtained byquantization of the luminance value of a video (content) by usinginverse EOTF of HDR that associates the luminance value in the luminancerange of HDR with the plurality of HDR code values.

In step S102, regarding the luminance value of HDR determined in stepS101, luminance converter 102 performs the first luminance conversionthat determines the display luminance value compatible with theluminance range of the display associated with the luminance value ofHDR in advance, and converts the luminance value of HDR compatible withthe HDR luminance range into the display luminance value compatible withthe luminance range of the display.

Before step S102, conversion apparatus 100 acquires content luminanceinformation including at least one of a maximum value of luminance (CPL:Content Peak luminance) of a video (content) and an average luminancevalue (CAL: Content Average luminance) of a video as informationregarding the HDR signal. CPL (first maximum luminance value) is, forexample, a maximum value of the luminance values of a plurality ofimages that constitute the HDR video. CAL is, for example, an averageluminance value which is an average of the luminance values of theplurality of images that constitute the HDR video.

In addition, before step S102, conversion apparatus 100 acquires thedisplay characteristic information on display apparatus 200 from displayapparatus 200. Note that the display characteristic information isinformation indicating the display characteristic of display apparatus200, such as a maximum value of luminance that display apparatus 200 candisplay (DPL), display mode (refer to later description) of displayapparatus 200, and input-output characteristic (EOTF supported by thedisplay apparatus).

In addition, conversion apparatus 100 may transmit recommended displaysetting information (refer to later description, and hereinaftersometimes referred to as “setting information”) to display apparatus200.

Next, inverse luminance converter 103 of conversion apparatus 100performs inverse luminance conversion according to the display mode ofdisplay apparatus 200. Accordingly, inverse luminance converter 103performs second luminance conversion that converts the luminance valuecompatible with the luminance range of the display, which is the secondluminance range, into the luminance value compatible with the luminancerange of SDR, which is the third luminance range (S103). Details will bedescribed later. That is, regarding the display luminance value obtainedin step S102, inverse luminance converter 103 performs the secondluminance conversion that determines the luminance value compatible withSDR (hereinafter referred to as “SDR luminance value”) as a thirdluminance value compatible with the luminance range of SDR with themaximum value of 100 nit associated with the display luminance value inadvance, and converts the display luminance value compatible with theluminance range of the display into the SDR luminance value compatiblewith the luminance range of SDR.

Then, inverse SDR EOTF converter 104 of conversion apparatus 100performs inverse SDR EOTF conversion to generate the pseudo HDR video(S104). That is, inverse SDR EOTF converter 104 uses inverse EOTF(Electro-Optical Transfer Function) of SDR (Standard Dynamic Range),which is third correspondence information that associates the luminancevalue in the luminance range of HDR with a plurality of third codevalues, to quantize the determined luminance value of SDR, determinesthe third code value obtained by quantization, and converts theluminance value of SDR compatible with the luminance range of SDR intothe SDR signal as a third luminance signal indicating the third codevalue, thereby generating the pseudo HDR signal. Here, each of the thirdcode values is a code value compatible with SDR, and hereinafterreferred to as “code value of SDR”. That is, the SDR signal is expressedby the code value of SDR obtained by quantization of the luminance valueof a video by using inverse EOTF of SDR that associates the luminancevalue in the luminance range of SDR with the plurality of code values ofSDR. Then, conversion apparatus 100 outputs the pseudo HDR signal (SDRsignal) generated in step S104 to display apparatus 200.

Conversion apparatus 100 performs the first luminance conversion and thesecond luminance conversion on the luminance value of HDR obtained byperforming inverse quantization on the HDR signal to generate theluminance value of SDR compatible with pseudo HDR. Conversion apparatus100 quantizes the luminance value of SDR by using EOTF of SDR togenerate the SDR signal compatible with pseudo HDR. Although theluminance value of SDR is a numerical value within the luminance rangeof 0 to 100 nit compatible with SDR, since conversion based on theluminance range of the display is performed, the luminance value of SDRis a numerical value different from the luminance value within theluminance range of 0 to 100 nit compatible with SDR obtained byperforming the luminance conversion using EOTF of HDR and EOTF of SDR onthe luminance value of HDR.

Next, the display method to be performed by display apparatus 200 willbe described with reference to FIG. 12. Note that the display methodincludes step S105 to step S108 described below.

First, display setting unit 201 of display apparatus 200 uses thesetting information acquired from conversion apparatus 100 to setdisplay settings of display apparatus 200 (S105). Here, displayapparatus 200 is the SDR TV. The setting information is informationindicating display settings recommended to the display apparatus, and isinformation indicating how to perform EOTF on the pseudo HDR video andwhich display settings to use for displaying a beautiful video (that is,information for switching the display settings of display apparatus 200to optimal display settings). The setting information includes, forexample, a gamma curve characteristic of output in the displayapparatus, display modes such as a living mode (normal mode) and dynamicmode, and a numerical value of a back light (brightness). In addition, amessage may be displayed on display apparatus 200 for prompting the userto change the display settings of display apparatus 200 (hereinaftersometimes referred to as “SDR display”) by manual operation. Detailswill be described later.

Note that, before step S105, display apparatus 200 acquires the SDRsignal (pseudo HDR signal) and the setting information indicating thedisplay settings recommended to display apparatus 200 in displaying avideo.

Display apparatus 200 only needs to acquire the SDR signal (pseudo HDRsignal) before step S106, and may acquire the SDR signal after stepS105.

Next, SDR EOTF converter 202 of display apparatus 200 performs EOTFconversion of SDR on the acquired pseudo HDR signal (S106). That is, SDREOTF converter 202 performs inverse quantization on the SDR signal(pseudo HDR signal) by using EOTF of SDR. Accordingly, SDR EOTFconverter 202 converts the code value of SDR indicated by the SDR signalinto the luminance value of SDR.

Then, luminance converter 203 of display apparatus 200 performs theluminance conversion according to the display mode that is set fordisplay apparatus 200. Accordingly, luminance converter 203 performsthird luminance conversion that converts the luminance value of SDRcompatible with the luminance range of SDR (0 to 100 [nit]) into thedisplay luminance value compatible with the luminance range of thedisplay (0 to DPL [nit]) (S107). Details will be described later.

As described above, in step S106 and step S107, display apparatus 200converts the third code value indicated by the acquired SDR signal(pseudo HDR signal) into the display luminance value compatible with theluminance range of the display (0 to DPL [nit]) by using the settinginformation acquired in step S105.

More specifically, in the conversion from the SDR signal (pseudo HDRsignal) into the display luminance value, in step S106, by using EOTFthat associates the luminance value in the luminance range of SDR withthe plurality of third code values, display apparatus 200 determines theluminance value of SDR associated with the code value of SDR indicatedby the acquired SDR signal by EOTF of SDR.

Then, in the conversion into the display luminance value, in step S107,display apparatus 200 performs the third luminance conversion thatdetermines the display luminance value compatible with the luminancerange of the display associated in advance with the determined luminancevalue of SDR, and converts the luminance value of SDR compatible withthe luminance range of SDR into the display luminance value compatiblewith the luminance range of the display.

Finally, display unit 204 of display apparatus 200 displays the pseudoHDR video on display apparatus 200 based on the converted displayluminance value (S108).

[1-13. First Luminance Conversion]

Next, details of the first luminance conversion (HPL to DPL) of stepS102 will be described with reference to FIG. 13A. FIG. 13A is a diagramillustrating an example of the first luminance conversion.

Luminance converter 102 of conversion apparatus 100 performs the firstluminance conversion of converting the linear signal (luminance value ofHDR) obtained in step S101 by using the display characteristicinformation and the content luminance information on the HDR video. Thefirst luminance conversion converts the luminance value of HDR (inputluminance value) into the display luminance value (output luminancevalue) that does not exceed the display peak luminance (DPL). DPL isdetermined using the maximum luminance of the SDR display and thedisplay mode which are the display characteristic information. Thedisplay mode is, for example, mode information including a theater modeof relatively dark display on the SDR display and a dynamic mode ofrelatively bright display. When the display mode is, for example, a modein which the maximum luminance of the SDR display is 1,500 nit, and thedisplay mode is a mode in which brightness is set to 50% of the maximumluminance, DPL will be 750 nit. Here, DPL (second maximum luminancevalue) is a maximum value of luminance the SDR display can display inthe display mode of current setting. That is, in the first luminanceconversion, DPL as the second maximum luminance value is determined byusing the display characteristic information which is informationindicating the display characteristic of the SDR display.

In addition, in the first luminance conversion, CAL and CPL out of thecontent luminance information are used. The luminance value equal to orless than vicinity of CAL is identical between before and after theconversion, and only the luminance value equal to or greater thanvicinity of CPL is changed. That is, as illustrated in FIG. 13A, in thefirst luminance conversion, when the luminance value of HDR is equal toor less than CAL, the luminance value of HDR is not converted, and theluminance value of HDR is determined as the display luminance value.When the luminance value of HDR is equal to or greater than CPL, DPL asthe second maximum luminance value is determined as the displayluminance value.

In addition, in the first luminance conversion, out of the luminanceinformation, the peak luminance of the HDR video (CPL) is used. When theluminance value of HDR is CPL, DPL is determined as the displayluminance value.

Note that, in the first luminance conversion, as illustrated in FIG.13B, conversion may be performed so that the linear signal (luminancevalue of HDR) obtained in step S101 may be clipped to a value that doesnot exceed DPL. Such luminance conversion can simplify processingperformed by conversion apparatus 100, and can achieve size reduction,low power consumption, and high-speed processing of the apparatus. Notethat FIG. 13B is a diagram illustrating another example of the firstluminance conversion.

[1-14. Second Luminance Conversion]

Next, details of the second luminance conversion of step S103 (DPL to100 [nit]) will be described with reference to FIG. 14. FIG. 14 is adiagram illustrating the second luminance conversion.

Inverse luminance converter 103 of conversion apparatus 100 appliesinverse luminance conversion according to the display mode to thedisplay luminance value in the luminance range of the display convertedin the first luminance conversion of step S102 (0 to DPL [nit]). Theinverse luminance conversion is processing for acquiring the displayluminance value in the luminance range of the display after processingof step S102 (0 to DPL [nit]) when the luminance conversion processing(step S107) according to the display mode is performed by the SDRdisplay. That is, the second luminance conversion is the inverseluminance conversion of the third luminance conversion.

By the aforementioned processing, the second luminance conversionconverts the display luminance value in the luminance range of thedisplay (input luminance value), which is the second luminance range,into the luminance value of SDR in the luminance range of SDR (outputluminance value), which is the third luminance range.

In the second luminance conversion, a conversion equation is switchedaccording to the display mode of the SDR display. For example, when thedisplay mode of the SDR display is the normal mode, the luminanceconversion is performed to a direct proportion value in directproportion to the display luminance value. In the second luminanceconversion, when the display mode of the SDR display is the dynamic modein which a high-luminance pixel becomes brighter and a low-luminancepixel becomes darker than pixels in the normal mode, the luminanceconversion is performed by using an inverse function thereof so that theluminance value of SDR of the low-luminance pixel is converted into avalue higher than the direct proportion value in direct proportion tothe display luminance value, and that the luminance value of SDR of thehigh-luminance pixel is converted into a value lower than the directproportion value in direct proportion to the display luminance value.That is, in the second luminance conversion, regarding the displayluminance value determined in step S102, by using luminance-relatedinformation according to the display characteristic information which isinformation indicating the display characteristic of the SDR display,the luminance value associated with the display luminance value isdetermined as the luminance value of SDR, and the luminance conversionprocessing is switched according to the display characteristicinformation. Here, the luminance-related information according to thedisplay characteristic information refers, for example as illustrated inFIG. 14, to information that associates the display luminance value(input luminance value) with the luminance value of SDR (outputluminance value) defined for each display parameter of the SDR display(display mode).

[1-15. Display Settings]

Next, details of the display settings of step S105 will be describedwith reference to FIG. 15. FIG. 15 is a flowchart illustrating detailedprocessing of the display settings.

In step S105, display setting unit 201 of the SDR display performs stepS201 to step S208 described below.

First, display setting unit 201 uses the setting information todetermine whether EOTF that is set for the SDR display (EOTF for SDRdisplay) is consistent with EOTF assumed at a time of generation of thepseudo HDR video (SDR signal) (S201).

When display setting unit 201 determines that EOTF that is set for theSDR display differs from EOTF indicated by the setting information (EOTFconsistent with the pseudo HDR video) (Yes in S201), display settingunit 201 determines whether EOTF for the SDR display is switchable on asystem side (S202).

When display setting unit 201 determines that EOTF for the SDR displayis switchable, display setting unit 201 uses the setting information toswitch EOTF for the SDR display to appropriate EOTF (S203).

From step S201 to step S203, in setting of the display settings (S105),display setting unit 201 sets EOTF that is set for the SDR display asrecommended EOTF according to the acquired setting information. Thisallows determination of the luminance value of SDR by using therecommended EOTF in step S106 to be performed after step S105.

When display setting unit 201 determines that EOTF for the SDR displayis not switchable on the system side (No in S202), display setting unit201 displays a message on a screen prompting the user to change EOTF bymanual operation (S204). For example, display setting unit 201 displaysa message on the screen saying “Set display gamma to 2.4”. That is, whendisplay setting unit 201 cannot switch EOTF that is set for the SDRdisplay in setting of the display settings (S105), display setting unit201 displays the message on the SDR display for prompting the user toswitch EOTF that is set for the SDR display (EOTF for the SDR display)to the recommended EOTF.

Next, although the SDR display displays the pseudo HDR video (SDRsignal), before the display, display setting unit 201 uses the settinginformation to determine whether the display parameter of the SDRdisplay matches the setting information (S205).

When display setting unit 201 determines that the display parameter thatis set for the SDR display differs from the setting information (Yes inS205), display setting unit 201 determines whether the display parameterof the SDR display is switchable (S206).

When display setting unit 201 determines that the display parameter ofthe SDR display is switchable (Yes in S206), display setting unit 201switches the display parameter of the SDR display in accordance with thesetting information (S207).

From step S204 to step S207, in setting of the display settings (S105),display setting unit 201 sets the display parameter that is set for theSDR display as a recommended display parameter according to the acquiredsetting information.

When display setting unit 201 determines that the display parameter ofthe SDR display is not switchable on the system side (No in S206),display setting unit 201 displays a message on the screen prompting theuser to change the display parameter that is set for the SDR display bymanual operation (S208). For example, display setting unit 201 displaysa message on the screen saying “Set display mode to dynamic mode, andincrease back light to maximum level”. That is, in setting (S105), whenthe display parameter that is set for the SDR display cannot beswitched, display setting unit 201 displays the message on the SDRdisplay for prompting the user to switch the display parameter that isset for the SDR display to the recommended display parameter.

[1-16. Third Luminance Conversion]

Next, details of the third luminance conversion of step S107 (100 to DPL[nit]) will be described with reference to FIG. 16. FIG. 16 is a diagramillustrating the third luminance conversion.

Luminance converter 203 of display apparatus 200 converts the luminancevalue of SDR in the luminance range of SDR (0 to 100 [nit]) into (0 toDPL [nit]) according to the display mode that is set in step S105. Thisprocessing is performed so as to become an inverse function of theinverse luminance conversion for each mode of S103.

In the third luminance conversion, the conversion equation is switchedaccording to the display mode of the SDR display. For example, when thedisplay mode of the SDR display is the normal mode (that is, when theset display parameter is a parameter compatible with the normal mode),the luminance conversion of the display luminance value is performed tothe direct proportion value in direct proportion to the luminance valueof SDR. In the third luminance conversion, when the display mode of theSDR display is the dynamic mode in which a high-luminance pixel becomesbrighter and a low-luminance pixel becomes darker than pixels in thenormal mode, the luminance conversion is performed so that the displayluminance value of the low-luminance pixel is converted into a valuelower than the direct proportion value in direct proportion to theluminance value of SDR, and that the display luminance value of thehigh-luminance pixel is converted into a value higher than the directproportion value in direct proportion to the luminance value of SDR.That is, in the third luminance conversion, regarding the luminancevalue of SDR determined in step S106, by using luminance-relatedinformation according to the display parameter indicating the displaysettings of the SDR display, the luminance value associated in advancewith the luminance value of SDR is determined as the display luminancevalue, and the luminance conversion processing is switched according tothe display parameter. Here, the luminance-related information accordingto the display parameter refers, for example as illustrated in FIG. 16,to information that associates the luminance value of SDR (inputluminance value) with the display luminance value (output luminancevalue) defined for each display parameter of the SDR display (displaymode).

[1-17. Advantageous Effects, etc.]

A normal SDR TV, whose input signal is 100 nit, has capability of visualrepresentation of 200 nit or more adapted to viewing environments (darkroom: cinema mode, bright room: dynamic mode, etc.). However, since aluminance upper limit of the input signal to the SDR TV is determined as100 nit, the capability cannot be used directly.

In a case of displaying the HDR video on the SDR TV, by making use ofthe fact that the peak luminance of the SDR TV for display exceeds 100nit (normally 200 nit or more), “HDR to pseudo HDR conversionprocessing” is performed so that gradation of the luminance rangeexceeding 100 nit be maintained to some extent, instead of conversion ofthe HDR video into the SDR video of 100 nit or less. Therefore, the HDRvideo may be displayed on the SDR TV as a pseudo HDR video close to theoriginal HDR video.

When this “HDR to pseudo HDR conversion processing” technique is appliedto Blu-ray with an HDR disc storing only the HDR signal and the SDR TVconnected to the Blu-ray device as illustrated in FIG. 17, the Blu-raydevice performs the “HDR to pseudo HDR conversion processing”, convertsthe HDR signal into the pseudo HDR signal, and sends the pseudo HDRsignal to the SDR TV. This allows the SDR TV to display a video with apseudo HDR effect by converting the received pseudo HDR signal into aluminance value. Thus, even where there is no HDR-enabled TV, when theHDR-enabled BD and HDR-enabled Blu-ray device are prepared, even the SDRTV can display the pseudo HDR video with higher display quality thanthat of the SDR video.

Therefore, although it has been considered that the HDR-enabled TV isrequired for watching the HDR video, the pseudo HDR video that providesfeeling of an HDR-like effect can be watched on the existing SDR TV.Accordingly, wide use of HDR-enabled Blu-ray is expected.

The HDR signal sent by broadcast, package media such as Blu-ray, andInternet delivery such as OTT is converted into the pseudo HDR signal byperforming the HDR-pseudo HDR conversion processing. This allows the HDRsignal to be displayed on the existing SDR TV as the pseudo HDR video.

Other Exemplary Embodiments

As described above, the exemplary embodiment has been described by wayof example of the technique to be disclosed in this application.However, the technique in the present disclosure is not limited to thisexample, and is also applicable to the exemplary embodiment to whichchange, replacement, addition, omission, etc. are made as appropriate.It is also possible to make a new exemplary embodiment by combiningcomponents described in the aforementioned exemplary embodiment.

Therefore, other exemplary embodiment will be illustrated below.

The HDR video is, for example, a video within a Blu-ray disc, DVD, videodelivery site on the Internet, broadcast, and HDD.

Conversion apparatus 100 (HDR to pseudo HDR conversion processor) mayexist within a disc player, disc recorder, set-top box, TV, personalcomputer, and smart phone.

Conversion apparatus 100 may exist within a server apparatus on theInternet.

Display apparatus 200 (SDR display unit) is, for example, a TV, personalcomputer, and smart phone.

The display characteristic information to be acquired by conversionapparatus 100 may be acquired from display apparatus 200 through an HDMIcable or LAN cable by using HDMI or other communication protocols. Asthe display characteristic information to be acquired by conversionapparatus 100, display characteristic information included in modelinformation on display apparatus 200, etc. may be acquired via theInternet. The user may perform manual operation to set the displaycharacteristic information in conversion apparatus 100. Acquisition ofthe display characteristic information by conversion apparatus 100 maybe performed immediately before pseudo HDR video generation (steps S101to S104), and may be performed with timing of initial setting of adevice or display connection. For example, acquisition of the displaycharacteristic information may be performed immediately beforeconversion into the display luminance value, and may be performed withtiming with which conversion apparatus 100 is connected to displayapparatus 200 with an HDMI cable for the first time.

One set of information items including CPL and CAL of the HDR video mayexist per one piece of content, and may exist for each scene. That is,in the conversion method may be acquired luminance information (CPL,CAL) compatible with each of a plurality of scenes in a video, theluminance information including, for each of the scenes, at least one ofa first maximum luminance value which is a maximum value out of theluminance values of a plurality of images that constitute the scene, andan average luminance value which is an average of the luminance valuesof the plurality of images that constitute the scene. In the firstluminance conversion, the display luminance value may be determined inaccordance with luminance information corresponding to each of theplurality of scenes.

CPL and CAL may be provided in a medium (such as a Blu-ray disc and DVD)identical to a medium of the HDR video, and may be acquired from a placedifferent from the HDR video, such as conversion apparatus 100 acquiresCPL and CAL from the Internet. That is, the luminance informationincluding at least one of CPL and CAL may be acquired as metadatainformation on the video, and may be acquired via a network.

In the first luminance conversion of conversion apparatus 100 (HPL toDPL), CPL, CAL, and the display peak luminance (DPL) may not be used,and fixed values may be used. The fixed values may be changeable fromoutside. CPL, CAL, and DPL may be switched among several types, forexample, DPL may be only three types including, 200 nit, 400 nit, and800 nit, and a value closest to the display characteristic informationmay be used.

EOTF of HDR may not be SMPTE 2084, and EOTF of HDR of another type maybe used. The maximum luminance of the HDR video (HPL) may not be 10,000nit, and may be, for example, 4,000 nit or 1,000 nit.

A bit width of the code value may be, for example, 16, 14, 12, 10, or 8bits.

Although inverse EOTF conversion of SDR is determined from the displaycharacteristic information, a fixed (changeable from outside) conversionfunction may be used. Inverse EOTF conversion of SDR may use, forexample, a function prescribed by Rec. ITU-R BT.1886. Types of inverseEOTF conversion of SDR may be limited to several types, and a typeclosest to an input-output characteristic of display apparatus 200 maybe selected and used.

A fixed mode may be used as the display mode, and the display mode maynot be included in the display characteristic information.

Conversion apparatus 100 may not transmit the setting information,display apparatus 200 may use fixed display settings, and may not changethe display settings. In this case, display setting unit 201 isunnecessary. The setting information may be flag information indicatingwhether a video is the pseudo HDR video, and for example, when a videois the pseudo HDR video, settings may be changed to brightest display.That is, in setting of the display settings (S105), when the acquiredsetting information indicates a signal indicating the pseudo HDR videothat is converted using DPL, brightness settings of display apparatus200 may be switched to settings of brightest display.

The first luminance conversion (HPL to DPL) of conversion apparatus 100is performed by the next formula, for example.

[Mathematical Expression 1]

$V = \left\{ \begin{matrix}L & \left. {{for}\mspace{14mu} 0}\Leftarrow{L < {S\; 1}} \right. \\{{a^{*}{\ln(L)}} + b} & \left. {{for}\mspace{14mu} S\; 1}\Leftarrow{L < {S\; 2}} \right. \\M & \left. {{for}\mspace{14mu} S\; 2}\Leftarrow L \right.\end{matrix} \right.$

Here, L denotes a luminance value normalized to 0 to 1, and S1, S2, a,b, and M are values to be set based on CAL, CPL, and DPL. In is anatural logarithm. V is a converted luminance value normalized to 0to 1. As in the example of FIG. 13A, when CAL is 300 nit, CPL is 2,000nit, DPL is 750 nit, conversion is not performed until CAL+50 nit, andconversion is performed for 350 nit or more, respective values are asfollows, for example.S1=350/10,000S2=2,000/10,000M=750/10,000a=0.023b=S1−a*ln(S1)=0.112105

That is, in the first luminance conversion, when the luminance value ofSDR is between the average luminance value (CAL) and the first maximumluminance value (CPL), the display luminance value corresponding to theluminance value of HDR is determined using a natural logarithm.

By converting the HDR video by using information including the contentpeak luminance and content average luminance of the HDR video, theconversion equation may be changed according to content, and it ispossible to perform conversion so that gradation of HDR may bemaintained as much as possible. It is also possible to inhibit anadverse effect such as too dark and too bright. Specifically, by mappingthe content peak luminance of the HDR video on the display peakluminance, gradation is maintained as much as possible. In addition,overall brightness is kept from changing by not changing a pixel valueequal to or less than vicinity of the average luminance.

By using the peak luminance value and the display mode of the SDRdisplay to convert the HDR video, the conversion equation may be changedin accordance with display environments of the SDR display. Inaccordance with performance of the SDR display, a video with feeling ofHDR (pseudo HDR video) may be displayed with gradation and brightnesssimilar to gradation and brightness of an original HDR video.Specifically, by determining the display peak luminance in accordancewith the maximum luminance and display mode of the SDR display, and byconverting the HDR video so as not to exceed the peak luminance value,the HDR video is displayed with little reduction in gradation of the HDRvideo until brightness that is displayable by the SDR display. Fornon-displayable brightness levels, the luminance value is decreased to adisplayable brightness level.

This makes it possible to reduce non-displayable brightness information,and to display video in a form close to the original HDR video withoutreducing gradation of displayable brightness. For example, for a displaywith a peak luminance of 1,000 nit, overall brightness is maintained byconversion into the pseudo HDR video with a peak luminance reduced to1,000 nit, and the luminance value changes depending on the display modeof the display. Therefore, the conversion equation of luminance ischanged according to the display mode of the display. If luminancegreater than the peak luminance of the display is allowed in the pseudoHDR video, such great luminance may be replaced with the peak luminanceon the display side for display. In this case, the display becomesdarker than the original HDR video on the whole. In contrast, when theconversion is performed with the luminance smaller than the peakluminance of the display as the maximum luminance, such small luminanceis replaced with the peak luminance on the display side, and the displaybecomes brighter than the original HDR video on the whole. Moreover,this does not make the most of performance regarding gradation of thedisplay because the luminance is smaller than the peak luminance on thedisplay side.

On the display side, this makes it possible to better display the pseudoHDR video by switching the display settings by using the settinginformation. For example, when brightness is set to dark, high-luminancedisplay is not possible, and thus feeling of HDR is impaired. In thiscase, by changing the display settings or by displaying a messageprompting to change the display settings, maximum performance of thedisplay is brought out, and a high-gradation video may be displayed.

In content such as Blu-ray, a video signal and a graphics signal, suchas subtitles and menus, are multiplexed as independent data. Duringplayback, each signal is decoded individually, and decoding results arecomposited and displayed. Specifically, a plane of subtitles or menus issuperimposed on a plane of the video.

Here, even if the video signal is HDR, the graphics signal of subtitlesor menus may be SDR. In HPL to DPL conversion of the video signal, thefollowing two kinds of conversion (a) and (b) are possible.

(a) When HPL to DPL conversion is performed after composition ofgraphics.

1. Convert EOTF of the graphics from EOTF of SDR into EOTF of HDR.

2. Composite the graphics after EOTF conversion with the video.

3. Perform HPL to DPL conversion on a composite result.

(b) When HPL to DPL conversion is performed prior to composition ofgraphics.

1. Convert EOTF of the graphics from EOTF of SDR into EOTF of HDR.

2. Perform HPL to DPL conversion on the video.

3. Composite the graphics after EOTF conversion with the video after DPLconversion.

For (b), order of 1 and 2 may be interchanged.

Although peak luminance of the graphics is 100 nit both in scheme (a)and scheme (b), for example, if DPL is high luminance as high as 1000nit, luminance of the graphics which remains 100 nit may lead toreduction in the luminance of the graphics of the video after HPL to DPLconversion. In particular, a bad influence is assumed such as darksubtitles superimposed on the video. Accordingly, the luminance of thegraphics may also be converted according to a value of DPL. For example,a rule of proportion of the luminance of subtitles to the DPL value maybe determined in advance, and the luminance of subtitles may beconverted based on a setting value. Graphics other than subtitles, suchas menus, can be processed similarly.

A playback operation of the HDR disc that stores only the HDR signal hasbeen described above.

Next, multiplex data to be stored in the dual disc that stores both theHDR signal and the SDR signal illustrated in Case 2 of FIG. 6B will bedescribed with reference to FIG. 18. FIG. 18 is a diagram illustratingthe multiplex data to be stored in the dual disc.

In the dual disc, as illustrated in FIG. 18, the HDR signal and the SDRsignal are stored as multiplex streams different from each other. Forexample, in an optical disc such as Blu-ray, data of a plurality ofmedia, such as video, audio, subtitles, and graphics, is stored as onemultiplex stream by an MPEG-2TS-based multiplexing scheme called M2TS.These multiplex streams are referenced from metadata for playbackcontrol, such as a play list. During playback, a player selects themultiplex stream to be played, or data of individual language stored inthe multiplex stream by analyzing the metadata. This example indicates acase where the play list for HDR and the play list for SDR are storedindividually, and where each play list references the HDR signal or theSDR signal. Identification information or the like indicating that boththe HDR signal and the SDR signal are stored may be indicatedseparately.

Although it is possible to multiplex both the HDR signal and the SDRsignal in an identical multiplex stream, it is necessary for suchmultiplexing to satisfy a buffer model, such as System Target Decoder(T-STD) prescribed in MPEG-2TS. In particular, it is difficult tomultiplex two videos with high bit rate within a range of apredetermined data reading rate. Therefore, preferably the multiplexstreams are separated.

It is necessary to store data of audio, subtitles, graphics, etc. ineach multiplex stream, and data volume increases as compared withmultiplexing in one stream. However, against the increase in the datavolume, the data volume of video can be reduced by using a video codingscheme with a high compression ratio. For example, changing MPEG-4 AVCused in conventional Blu-ray into High Efficiency Video Coding (HEVC) isexpected to provide improvement in the compression ratio by a factor of1.6 to 2. Only a combination that fits into capacity of an optical discmay be allowed to be stored in a dual disc, such as storing acombination of two 2K streams or a combination of a 4K stream and a 2Kstream, including a combination of a 2K HDR stream and a 2K SDR stream,and a combination of a 4K SDR stream and a 2K HDR stream, by prohibitingstorage of two 4K streams.

FIG. 19 is a flowchart illustrating a playback operation of the dualdisc.

First, the playback apparatus determines whether an optical disc to beplayed is a dual disc (S301). When it is determined that the opticaldisc to be played is a dual disc (Yes in S301), the playback apparatusdetermines whether an output destination TV is an HDR TV or SDR TV(S302). When it is determined that the TV is an HDR TV (Yes in S302),the processing advances to step S303. When it is determined that the TVis an SDR TV (No in S302), the processing advances to step S304. In stepS303, the playback apparatus acquires a video signal of HDR from themultiplex stream including the HDR signal within the dual disc, anddecodes and outputs the video signal to the HDR TV. In step S304, theplayback apparatus acquires a video signal of SDR from the multiplexstream including the SDR signal within the dual disc, and decodes andoutputs the video signal to the SDR TV. When it is determined in stepS301 that the optical disc to be played is not a dual disc (No in S301),the playback apparatus determines whether playback is possible by apredetermined method, and decides a playback method based on a result ofthe determination (S305).

In a case of displaying the HDR video on the SDR TV in the conversionmethod of the present disclosure, by making use of the fact that thepeak luminance of the SDR TV for display exceeds 100 nit (normally 200nit or more), “HDR to pseudo HDR conversion processing” is implementedthat allows conversion of the HDR video into a pseudo HDR video similarto an original HDR and display on the SDR TV, by converting the HDRvideo while maintaining gradation of a region exceeding 100 nit to someextent, instead of conversion of the HDR video into the SDR video of 100nit or less.

In this conversion method, the conversion method of the “HDR to pseudoHDR conversion processing” may be switched in accordance with thedisplay characteristic of the SDR TV (maximum luminance, input-outputcharacteristic, and display mode).

Conceivable acquisition methods of display characteristic informationinclude (1) automatic acquisition through HDMI or a network, (2)generation by causing the user to input information such as amanufacturer name and model number, and (3) acquisition from a cloud,etc. using the information such as the manufacturer name and the modelnumber.

Conceivable acquisition timing of the display characteristic informationby conversion apparatus 100 includes (1) acquisition immediately beforepseudo HDR conversion, and (2) when connected to display apparatus 200(such as the SDR TV) for the first time (when the connection isestablished).

In this conversion method, the conversion method may be switched inaccordance with luminance information on the HDR video (CAL, CPL).

Examples of the conceivable acquisition method of the luminanceinformation on the HDR video by conversion apparatus 100 include (1)acquisition as metadata information appended to the HDR video, (2)acquisition by causing the user to input title information on content,and (3) acquisition from a cloud, etc. using input information that isinput by the user.

Details of the conversion method include (1) conversion so that theluminance would not exceed DPL, (2) conversion so that CPL would becomeDPL, (3) not changing the luminance equal to or less than CAL andvicinity thereof, (4) conversion using a natural logarithm, and (5) clipprocessing at DPL.

In order to enhance an effect of pseudo HDR, this conversion method mayinclude transmitting display settings such as a display mode and displayparameter of the SDR TV to display apparatus 200 for switching. Forexample, a message prompting the user to make display settings may bedisplayed on a screen.

In the aforementioned exemplary embodiment, each component may be madeof dedicated hardware, or may be implemented through execution of asoftware program suitable for each component. Each component may beimplemented by a program execution unit, such as a CPU or a processor,reading and executing the software program recorded in a recordingmedium such as a hard disk or a semiconductor memory.

Although the display method and the display apparatus according to oneor more aspects of the present disclosure have been described above onthe basis of the exemplary embodiment, the present disclosure is notlimited to this exemplary embodiment. The exemplary embodiment to whichvarious modifications conceivable by a person skilled in the art aremade, and aspects that are made by combining elements of differentexemplary embodiment may also be within the scope of the one or moreaspects of the present disclosure as long as such aspects do not departfrom the gist of the present disclosure.

The present disclosure is useful as a conversion method, conversionapparatus, and the like that can appropriately convert luminance in thefirst luminance range into luminance in the second luminance range withreduced luminance range.

What is claimed is:
 1. A conversion method for converting luminance of avideo to be displayed on a display apparatus, the conversion methodcomprising: acquiring a first luminance signal indicating a first codevalue obtained by quantization of a luminance value of the video, theluminance value of the video being included in a first luminance range;and converting the first code value indicated by the acquired firstluminance signal into a second luminance value compatible with a secondluminance range, a maximum value of the second luminance range beingdetermined based on a luminance range of the display apparatus, themaximum value of the second luminance range being smaller than a maximumvalue of the first luminance range, and the maximum value of the secondluminance range being larger than 100 nit; wherein: the converting thefirst code value comprises: by using an electro-optical transferfunction (EOTF) that associates the luminance value in the firstluminance range with a plurality of first code values, determining afirst luminance value associated with the first code value indicated bythe acquired first luminance signal, the first luminance value beingcompatible with the first luminance range; determining the secondluminance value associated with the first luminance value in advance,the second luminance value being compatible with the second luminancerange; and performing first luminance conversion to convert the firstluminance value compatible with the first luminance range into thesecond luminance value compatible with the second luminance range; themaximum value of the second luminance range is a maximum value of theluminance range of the display apparatus; the performing the firstluminance conversion comprises, when the first luminance value is afirst maximum luminance value that is a maximum value of luminancevalues of a plurality of images that constitute the video, determining asecond maximum luminance value that is the maximum value of theluminance of the display apparatus as the second luminance value; andwherein the performing the first luminance conversion comprises: whenthe first luminance value is equal to or less than a predeterminedluminance value, converting the first luminance value into the secondluminance value so that a relationship between the first luminance valueand second luminance value is linear.
 2. A conversion apparatus forconverting luminance of a video to be displayed on a display apparatus,the conversion apparatus comprising: one or more memories; and circuitrywhich, in operation performs: acquiring a first luminance signalindicating a first code value obtained by quantization of a luminancevalue of the video, the luminance value of the video being included in afirst luminance range; and converting the first code value indicated bythe acquired first luminance signal into a second luminance valuecompatible with a second luminance range, a maximum value of the secondluminance range being determined based on a luminance range of thedisplay apparatus, the maximum value of the second luminance range beingsmaller than a maximum value of the first luminance range, and themaximum value of the second luminance range being larger than 100 nit;wherein: the converting the first code value comprises: by using anelectro-optical transfer function (EOTF) that associates the luminancevalue in the first luminance range with a plurality of first codevalues, determining a first luminance value associated with the firstcode value indicated by the acquired first luminance signal, the firstluminance value being compatible with the first luminance range;determining the second luminance value associated with the firstluminance value in advance, the second luminance value being compatiblewith the second luminance range; and performing first luminanceconversion to convert the first luminance value compatible with thefirst luminance range into the second luminance value compatible withthe second luminance range; the maximum value of the second luminancerange is a maximum value of the luminance range of the displayapparatus; the performing the first luminance conversion comprises, whenthe first luminance value is a first maximum luminance value that is amaximum value of luminance values of a plurality of images thatconstitute the video, determining a second maximum luminance value thatis the maximum value of the luminance of the display apparatus as thesecond luminance value; and wherein the performing the first luminanceconversion comprises: when the first luminance value is equal to or lessthan a predetermined luminance value, converting the first luminancevalue into the second luminance value so that a relationship between thefirst luminance value and second luminance value is linear.